Nowadays, in relation to health effects of smoking, a technique for reducing a harmful component in cigarette smoke is demanded in the cigarette field. Cigarette smoke contains various harmful components. Above all, a phenol compound such as phenol or cresol is a harmful substance which is contained in a relatively high concentration in the smoke, and effective removal of the phenol compound is desired. In order to adsorb the harmful substance, an activated carbon is widely used conventionally. However, physical adsorption, typically using an activated carbon, removes not only the harmful substance but also a palatable component in cigarette smoke. In other words, removal of nicotine, tar, and other flavor components changes the taste of cigarette smoke, so that a feeling of satisfaction in smoking is inhibited. Moreover, the activated carbon has a low capacity to adsorb the phenol compound. As a technique for producing a cigarette filter by adding an activated carbon to a tow comprising a cellulose acetate, the following technique is usually applied: a tow having a crimp undergo a tension between two pairs of rollers, each moving at a different speed, to be stretched, and the resulting tow is sprinkled with a charcoal, and then the charcoal is attached to the tow with a plasticizer such as triacetin to give a cigarette filter. However, according to this technique, the amount of the activated carbon attached is difficult to increase. In addition, the activated carbon adsorbs triacetin, so that the adsorbing capacity of the activated carbon is decreased.
On the other hand, currently, a cellulose acetate tow is commonly used for a cigarette filter. Although a filter made from the cellulose acetate tow can reduce a phenol content of mainstream cigarette smoke, the reduction is unsatisfactory. Thus, a method for selectively adsorb a phenol compound from mainstream cigarette smoke by a filter made from a cellulose acetate tow is desired.
Japanese Application Laid-Open No. 2001-526913 publication (JP-2001-526913A, Patent Document 1) discloses a cigarette filter which contains a polyphenol compound or a derivative thereof (such as an extract of rosemary) as a free-radical scavenger for removing a cytotoxic molecule having a free radical existing in cigarette smoke. Moreover, Japanese Patent No. 3910175 publication (JP-3910175B, Patent Document 2) discloses a cigarette filter for removing a phenol compound in mainstream smoke, the filter comprising the following three filter sections (A) to (C): (A) a filter section added with a liquid fatty acid ester or a liquid fatty acid, having a viscosity of 1 to 300 cP, (B) a filter section added with a glycol having a viscosity of 1 to 300 cP, and (C) a filter section added with an activated carbon and provided on a downstream side of the filter section (A) and the filter section (B).
However, in these cigarette filters, since the liquid substances are added to these filters, the liquid substances are scattered or moved to a tobacco-leaf zone during cigarette storage.
Japanese Patent Application Laid-Open No. 2006-191813 publication (JP-2006-191813A, Patent Document 3) discloses a smoking article for reducing a CO concentration and a NOx concentration in mainstream cigarette smoke. The smoking article comprises a rod-like core, a sheath formed by surrounding the core with shredded tobacco, and a tube covering the sheath, the core comprises a porous material charged in a partial portion or all portions of the core in a longitudinal direction thereof, and the air resistance (or draw resistance) of the core is lower than that of the sheath. The document discloses alumina, silica, and zeolite as a raw material for the porous material.
In the smoking article, the porous material is used not for a filter but for a tobacco-leaf zone, so that the porous material inevitably comprises an inorganic material. However, the inorganic material insufficiently adsorbs a phenol compound.
As a material for selectively and efficiently removing an aldehyde (in particular, formaldehyde) while maintaining a palatable component such as nicotine or tar, Japanese Patent Application Laid-Open No. 2008-154509 publication (JP-2008-154509A, Patent Document 4) discloses a cigarette filter material which comprises a porous material having an average pore size of 5 to 350 nm, such as a silica gel. Japanese Patent Application Laid-Open No. 2010-35550 publication (JP-2010-35550A, Patent Document 5) discloses a cigarette filter material which comprises a porous silica having a total nitrogen content of not more than 1% by weight, a total carbon content of not more than 20% by weight, an average pore size of 2 to 50 nm, a specific surface area of 500 to 1300 m2/g, and a pore of a hexagonal structure. According to these documents, a produced filter has a triplet structure that a gap in the divided filter is filled with the filter material.
However, damage to these filters having a triplet structure involves a risk of getting a scattered particulate porous material in the eyes or the lungs. Moreover, the triplet structure cannot improve the filter hardness.
On the other hand, as a filter mainly comprising a cellulose having a paper structure, Japanese Patent No. 3576222 publication (JP-3576222B, Patent Document 6) discloses a cigarette filter material in the form of a sheet which comprises a particulate or non-crimped fibrous cellulose ester and a wood pulp having a Canadian standard freeness value of 100 to 800 ml in a ratio of the former/the latter=15/85 to 80/20 (% by weight).
However, since the main body of this filter comprises the wood pulp (cellulose), the filter has an insufficient phenol removal and a low filter hardness. Moreover, although the filter hardness can be improved by increasing the ratio of the particulate cellulose ester relative to the wood pulp, the pressure drop is also increased. Thus, there is a limit in weight increase of the particulate cellulose ester. Further, the particulate cellulose ester is easily eliminated from the filter.
[Patent Document 1] JP-2001-526913A (Claims and Examples)
[Patent Document 2] JP-3910175B (Claim 1 and Examples)
[Patent Document 3] JP-2006-191813A (Claim 1 and Paragraphs [0011] and [0013])
[Patent Document 4] JP-2008-154509A (Claims, Paragraphs [0001] and [0044], and Examples)
[Patent Document 5] JP-2010-35550A (Claims, Paragraphs [0001] and [0054], and Examples)
[Patent Document 6] JP-3576222B (Claim 1)